So if you've lived through the early '90s you've heard the song Girls & Boys by Blur. It seemed like a modern song at the time, but the African bat bug got there long before the band did. In this group of bugs, each sex is imitating the other, and making sexual advances, in a never ending game of sexual one-upmanship.

Bugs are not known for their beautiful courtship rituals. One of their least attractive mating procedures is something called "traumatic insemination." A male approaches a female, extends his needle-like genitalia, and stabs her through the abdomen. The sperm travels through the blood and inseminates the female... or the wound kills her. Keep in mind that this is not the only way to have sex with a female bug, even in the species that practice traumatic insemination. The females have sexual tracts. They're just rarely used. African bat bugs, the bat's version of bed bugs, have it so bad that colonies in a laboratory — which have restricted space for the females to hide — will go completely extinct. Before they do go extinct, the males will have a tough time of it. While most male bat bugs will mount — but not mate with — male bugs, the African bat bug will mate with a male or a female, though it will mate with a female more readily and with more frequency.

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So perhaps it's no surprise that male and female African bat bugs have a similar adaptation. Female bugs develop a spermalege. A spermalege is a set of external grooves that guide males to their genitalia. Male Africa bat bugs had their own imitation of the spermalege, but it was especially thick and tough — since they did not have the genitalia that female bugs have — and lead to the least critical parts of their body. When researchers took another look at the species, they found that many of the bugs they had thought were males, due to the configuration of the spermalege, were actually females.

Scientists think the species evolved in this way. Males mated with both females and males, often causing death. Females developed a spermalege to cut down on traumatic stabbings that endangered their lives. Males developed a similar system in order to guide the other males' genitalia to a relatively non-critical area. A few females then developed external genitalia like those of males. The decreased attention they received from other males made them more likely to survive to procreate multiple times. Eventually, about five out of six females were imitating males — which may be one of the reasons why African bat bugs are more likely to mate with males.